Absorption cycle system having dual absorption circuits

ABSTRACT

An absorption cycle system utilizes an additional absorption circuit in conjunction with a traditional absorption circuit. The absorbent used in the additional absorption circuit could contain an ionic compound, or any absorbent with relatively low crystallization. Mixtures of such absorbent with water remain liquid at temperatures lower than the minimum feasible operating temperature of the traditional lithium bromide water absorbent solutions of the prior art.

BACKGROUND

1. Field of the Disclosure

The present disclosure relates to an absorption cycle system which hasdual absorption circuits. Such a system is useful in a wide range ofabsorption cycle applications including low temperature refrigeration,comfort air conditioning and space heating.

2. Description of Related Art

Single effect absorption cycle systems with a single absorption circuitare known in the art. In a typical absorption cycle system, arefrigerant, such as water vapor, is absorbed into an absorbent mixture,such as an aqueous lithium bromide (LiBr) solution, and then is releasedout of the absorbent mixture. The absorber is part of a singleabsorption circuit, which includes a pump, a heat exchanger, anexpansion or pressure reduction device and a generator, where therefrigerant is released from the absorbent mixture before it enters acondenser and an evaporator.

However, a drawback of such a standard system, which typically useslithium bromide and water as the absorbent/refrigerant pair, is that theminimum feasible absorber operating temperature is limited by thecrystallization temperature of the absorbent/refrigerant mixture.

It would be desirable to find suitable absorption cycle configurationsand corresponding absorbent/refrigerant mixtures, in particularabsorbent/water mixtures, which allow (for example, as a result ofresisting crystallization) the refrigerant returning from the evaporatorto be absorbed at a temperature lower than the minimum feasible absorberoperating temperature of an absorber which uses a lithium bromide/watersolution as the absorbent/refrigerant mixture.

SUMMARY

It is an object of the present invention to provide an absorption cyclesystem which utilizes an additional absorption circuit in conjunctionwith a traditional absorption circuit. The absorbent used in theadditional absorption circuit could be any absorbent whoseabsorbent/refrigerant mixtures are more advantageous at low temperatures(for example, as a result of resisting crystallization) compared to theabsorbent used in the traditional absorption circuit. The absorbent usedin the additional absorption circuit could be or could contain an ioniccompound or other crystallization suppressing additives. Mixtures ofsuch absorbent with water at compositions effective for the cycleoperation resist crystallization at temperatures lower than the minimumfeasible operating temperature of the traditional lithium bromide/watersolutions of the prior art.

With such a system, the additional absorber can be operated at lowertemperatures than a traditional absorber which circulates lithiumbromide and water as the absorbent/refrigerant mixture. A lower feasibleabsorber operating temperature is expected to enable novel cooling andheating applications especially for low ambient temperatures. A lowerfeasible absorber operating temperature is expected to also enablehigher cycle energy efficiency, which is expressed in the industry as ahigher coefficient of performance, or COP.

In addition, the use of two absorption circuits allows the simultaneoususe of thermally sensitive absorbents (such as thermally sensitive ioniccompounds or absorbent formulations containing thermally sensitivecrystallization suppressants or other thermally sensitive additives) inone circuit and high-temperature heat sources in the other circuit.

Therefore, in accordance with the present invention, there is providedan absorption cycle system comprising an evaporator for circulating arefrigerant therethrough, a first absorption circuit disposed in fluidcommunication with the evaporator for mixing the refrigerant from theevaporator with a first absorbent, thereby forming a first absorbent andrefrigerant mixture, and for circulating the first absorbent andrefrigerant mixture therethrough; a second absorption circuit disposedin fluid communication with the first absorption circuit for mixing aportion of the refrigerant from the first absorption circuit with asecond absorbent, thereby forming a second absorbent and refrigerantmixture, and for circulating the second absorbent and refrigerantmixture therethrough, and a condenser disposed in fluid communicationwith the second absorption circuit and with the evaporator. Thefirst-absorbent/refrigerant mixture resists crystallization, andtherefore remains operational, at temperatures lower than thesecond-absorbent/refrigerant mixture that circulates in the secondabsorption circuit.

According to another embodiment of the present invention, some of theheat from the high pressure refrigerant vapor may be recovered andtransferred to the first generator, instead of being rejected at thecondenser. This results in higher energy efficiency. Thus, in accordancewith this embodiment, the absorption cycle system of the presentinvention includes a heat recovery line extending between the secondgenerator and through the first generator for recovering heat from therefrigerant exiting the second generator. The heat recovery linecontinues from the first generator to the condenser, for delivering therefrigerant vapor to the condenser.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be better understood with reference to thefollowing Figures, wherein:

FIG. 1 is a schematic diagram of an absorption cycle system according toone embodiment of the present invention.

FIG. 2 is a schematic diagram of an absorption cycle system according toanother embodiment of the present invention.

DETAILED DESCRIPTION

A schematic diagram of an absorption cycle system according to thepresent invention is shown generally at 10 in FIG. 1. The system isfirst described as an absorption cooling system with respect to FIG. 1.The system includes an evaporator 10-1 for circulating a refrigeranttherethrough, a first absorption circuit, shown generally at 20 in FIG.1, disposed in fluid communication with the evaporator, for mixing therefrigerant from the evaporator with a first absorbent, thereby forminga first absorbent and refrigerant mixture, and for circulating the firstabsorbent and refrigerant mixture therethrough, a second absorptioncircuit, shown generally at 30 in FIG. 1, disposed in fluidcommunication with the first absorption circuit, for mixing a portion ofthe refrigerant from the first absorption circuit with a secondabsorbent, thereby forming a second absorbent and refrigerant mixtureand for circulating the second absorbent and refrigerant mixturetherethrough, and a condenser 10-2 disposed in fluid communication withthe second absorption circuit and the evaporator.

The evaporator of the system of the present invention includes an inletline 14 for delivering a refrigerant to the evaporator. The refrigerantin the system of the present invention as described below is water, itbeing understood that other refrigerants may be used in this system, aswill be described below. The refrigerant is partially evaporated liquidwhen it enters the evaporator. The evaporator, in some embodiments, alsoincludes tubes (not shown) through which flows chilled water or otherheat transfer fluid. The partially evaporated refrigerant contacts thetubes in the evaporator, and the liquid portion of the refrigerant isevaporated, thereby absorbing heat and forming refrigerant vapor. Thechilled water exits the evaporator through an outlet line 11 at atemperature lower than the temperature at which it entered theevaporator and is sent to a body to be cooled, such as a building, shownat 10-4 in FIG. 1. A body to be cooled may be any space, location,object or body which it is desirable to cool, including the interiorspaces of buildings requiring air conditioning, and refrigerator orfreezer spaces, in for instance hotels or restaurants, or industrialprocess areas for example used to process or produce food products.

The chilled water from the building is delivered back to the evaporatorthrough a line 12, and is recirculated through the tubes in theevaporator. The refrigerant vapor, exits the evaporator through a line13 as shown in FIG. 1, and is sent to the first absorption circuit 20via this line.

The first absorption circuit 20 comprises a first absorber 20-1, aliquid pump 20-2, a first heat exchanger 20-3 and a first, or lowtemperature, generator 20-4. The first absorber has an inlet fordelivering the refrigerant vapor, where it is combined with a mixture ofrefrigerant and a first absorbent with a low refrigerant-contentdelivered via line 25 to form a first-absorbent/refrigerant mixture witha high refrigerant-content. The first absorbent may be or may contain anionic compound. The absorption of the refrigerant into the firstabsorbent also, in general, generates heat (heat of absorption). Coolingwater or another heat transfer fluid circulates through the tube bundles(not shown) of the absorber to collect this heat of absorption from thesystem. The high refrigerant-content mixture collects at the bottom ofthe first absorber, so that the first absorption cycle can begin again.

The high refrigerant-content first-absorbent/refrigerant mixture exitsfrom the first absorber through an outlet line 21 and is sent to theliquid pump, 20-2, which pumps the said mixture to the first heatexchanger 20-3. The first heat exchanger, which may be a shell and tubetype heat exchanger, pre-heats the mixture before it enters the first orlow temperature generator. After exiting the heat exchanger, the mixtureflows into the first generator through a line 22. The first generator issupplied with low-temperature heat from any suitable external source. Inone embodiment, within the generator is a bundle of tubes (not shown)which carry a heat transfer fluid which may be hot water, steam, orcombustion gases, which are supplied to the first generator via a line23. The heat transfer fluid transfers heat into the highrefrigerant-content first-absorbent/refrigerant mixture. The heat causesthe said mixture to release refrigerant vapor, which exits from thefirst generator through a line 26, leaving a low refrigerant-contentmixture behind. The refrigerant is now a higher pressure vapor. In someinstances, there is only trace refrigerant left in the liquid mixtureexiting the first generator via a line 24. In other instances somenon-negligible amount of refrigerant remains in theabsorbent/refrigerant mixture exiting the first generator, said amountranging from about 1 weight percent to about 80 weight percent. In anycase, the amount of refrigerant in the mixture exiting the firstgenerator via line 24 is lower than in the mixture that exited the firstabsorber via line 21. The exact amount of refrigerant remaining in themixture exiting the first generator will depend on many factorsincluding the solubility of the refrigerant in the first absorbent.

The low refrigerant-content first-absorbent/refrigerant mixture flowsvia line 24 back to the first heat exchanger where it is cooled by thehigh refrigerant-content first-absorbent/refrigerant mixture which hasbeen pumped out of the first absorber. The low refrigerant-contentfirst-absorbent/refrigerant mixture flows from the first heat exchangerthrough an expansion or pressure reduction device 20-5 to the firstabsorber via a line 25 and collects in the bottom of the first absorberwhere it started the first absorption circuit cycle, and the cycle inthe first absorption circuit repeats.

The second absorption circuit includes a second absorber 30-1, a secondliquid pump 30-2, a second heat exchanger 30-3 and a second, or hightemperature generator 30-4. As noted above, the refrigerant vapor fromthe first absorption circuit exits the first generator and is deliveredto the second absorption circuit via a line 26. The refrigerant vapor isdelivered to second absorber 30-1, which includes tube bundles (notshown). A low refrigerant-content mixture of refrigerant and a secondabsorbent is also delivered to the second absorber via a line 35. Therefrigerant and the second absorbent collect in the bottom of the secondabsorber. Lithium bromide may be used as the second absorbent in thissystem, it being understood that the present invention is not limited tothe use of lithium bromide as the second absorbent. Again, as in thefirst absorber, the refrigerant vapor is absorbed into the lowrefrigerant-content second-absorbent/refrigerant mixture, thus forming ahigh refrigerant-content second-absorbent/refrigerant mixture. Theabsorption of the refrigerant into the second absorbent also, ingeneral, generates heat (heat of absorption). A heat transfer fluid, forinstance, cooling water, circulates through the tube bundles of thesecond absorber to collect this heat of absorption from the system.

Second pump 30-2 pumps the high refrigerant-contentsecond-absorbent/refrigerant mixture via a line 31 to the second heatexchanger 30-3, which, like the first heat exchanger, may be a shell andtube type heat exchanger. The second heat exchanger pre-heats the saidmixture before it enters the second generator 30-4 via a line 32. Thesecond generator is supplied with high-temperature heat from anysuitable external source. In one embodiment, within the second generatoris a bundle of tubes which carry a heat transfer fluid, which may be,for instance, combustion gases, steam, or hot water, which is suppliedto the second generator via a line 33. In some embodiments, the heattransfer fluid may have been heated to high temperatures through aconcentrated solar thermal system. The heat transfer fluid transfersheat into the high refrigerant-content second-absorbent/refrigerantmixture. The heat causes the said mixture to release refrigerant vapor,which exits from the second generator through a line 36, leaving a lowrefrigerant-content mixture behind in the second generator. Therefrigerant is now a high pressure vapor, which exits the generator vialine 36. The low refrigerant-content, second-absorbent/refrigerantmixture flows via line 34 back to the second heat exchanger where it iscooled by the high refrigerant-content second-absorbent/refrigerantmixture, which has been pumped out of the second absorber to the secondheat exchanger. The low refrigerant-content second-absorbent/refrigerantmixture flows from the second heat exchanger through an expansion orpressure reduction device 30-5 to the second absorber via a line 35 andcollects in the bottom of the second absorber, where it started thesecond absorption circuit cycle, and the second absorption circuit cyclerepeats. As in the first absorption circuit, the amount of refrigerantin the mixture exiting the second generator via line 34 is lower than inthe mixture that exited the second absorber via line 31, and can rangefrom a trace amount or more commonly from about 1 weight percent toabout 80 weight percent. The exact amount of refrigerant remaining inthe mixture exiting the second generator will depend on many factorsincluding the solubility of the refrigerant in the second absorbent.

As noted above, the refrigerant, which is a high pressure vapor, exitsthe second generator 30-4 via line 36. The high pressure refrigerantvapor flows to the condenser 10-2 as shown in FIG. 1. In the condenser,the heat transfer fluid, such as cooling water, flows through tubes (notshown) in the condenser, and the refrigerant vapor condenses to formrefrigerant liquid on the outside of the tubes that collects in a trough(not shown) at the bottom of the condenser. In other condenser designsthe released heat could be supplied to building air instead of to theheat transfer fluid, it being understood that various other condenserdesigns are within the scope of the present invention. The refrigerantliquid exits from the condenser trough via inlet line 14 to theevaporator through an expansion or pressure reduction device 10-3 thatpartially evaporates the refrigerant liquid. The partially evaporatedrefrigerant liquid contacts the tubes of the evaporator which have wateror some other heat transfer fluid flowing therethrough. The heattransfer fluid is cooled as the liquid refrigerant is evaporated formingrefrigerant vapor. The cooled heat transfer fluid is circulated back toa body to be cooled, such as a building, thus providing the coolingeffect as desired for instance for air conditioning. The refrigerantvapor migrates from the evaporator to the first absorber, and theoverall refrigerant cycle repeats.

Instead of being run as an absorption cooling system as described above,the system of FIG. 1 may be used as a heat pump. In this case, thesystem is an absorption heating system in which the heat supplied by thecycle in FIG. 1 at the first absorber, the second absorber and thecondenser is used to meet various heating needs such as heating buildingair or water. As noted above, the refrigerant, which is a high pressurevapor, exits the second generator 30-4 via line 36. The high pressurerefrigerant vapor flows to the condenser 10-2 as shown in FIG. 1. In thecondenser, cooling water or other heat transfer fluid flows throughtubes (not shown) in the condenser, and the refrigerant vapor condensesto form refrigerant liquid on the outside of the tubes that collects ina trough (not shown) at the bottom of the condenser. Upon condensationof the refrigerant vapor heat is released. In other condenser designsthe released heat could be supplied to building air instead of to thecooling water, it being understood that various other condenser designsare within the scope of the present invention. The refrigerant liquidexits from the condenser trough via inlet line 14 to the evaporatorthrough an expansion or pressure reduction device 10-3 that partiallyevaporates the refrigerant liquid. The refrigerant is partiallyevaporated liquid when it enters the evaporator. In some embodiments,the evaporator also includes tubes (not shown) through which flows wateror other heat transfer fluid supplying the evaporator with heatharvested from a source external to the cycle system such as water atthe bottom of a lake or a pond or the ground at depths below the earth'ssurface where temperatures remain moderate throughout the year or lowtemperature waste process heat. The evaporator may receive heat from theambient air. The partially evaporated refrigerant contacts the tubes inthe evaporator, and the liquid portion of the refrigerant is evaporated,thereby absorbing heat and forming refrigerant vapor. The heat transferfluid exits the evaporator through an outlet line 11 at a temperaturelower than the temperature at which it entered the evaporator and issent back to the external heat source, which in this embodiment is inplace of the building shown at 10-4 in FIG. 1. In this embodiment, thereis no longer exchange of heat between chilled water and a building to becooled, but rather between the water or heat transfer fluid thatsupplies heat to the evaporator and the external heat source. In thiscase, the heat transfer fluid from the external heat source is deliveredback to the evaporator through a line 12.

FIG. 2 shows a second embodiment of an absorption cooling system of thepresent invention. Such a system is generally shown at 110. The systemincludes an evaporator 110-1 disposed in fluid communication with afirst absorption circuit, shown generally at 120 in FIG. 2, a secondabsorption circuit, shown generally at 130 in FIG. 2, disposed in fluidcommunication with the first absorption circuit, and a condenser 110-2disposed in fluid communication with the second absorption circuit andthe evaporator.

The evaporator of the system of the present invention includes an inletline 114 for delivering a refrigerant to the evaporator. Again, therefrigerant in the system of the second embodiment of the presentinvention is water, it being understood that other refrigerants may beused in this system. The evaporator of the second embodiment operates inthe same way that the evaporator of FIG. 1 does. Thus, refrigerant ispartially evaporated liquid when it enters the evaporator. Theevaporator also includes tubes (not shown) through which flows chilledwater or other heat transfer fluid. The partially evaporated refrigerantcontacts the tubes in the evaporator, and the liquid portion of therefrigerant is evaporated, thereby absorbing heat and formingrefrigerant vapor. The chilled water exits the evaporator through anoutlet line 111 at a temperature lower than the temperature at which itentered the evaporator and is sent to a body to be cooled, such as abuilding, shown at 110-4 in FIG. 2.

The chilled water from the building is delivered back to the evaporatorthrough a line 112, and is recirculated through the tubes in theevaporator. The refrigerant vapor exits the evaporator through a line113 as shown in FIG. 2, and is sent to the first absorption circuit 120via this line.

The first absorption circuit 120 comprises a first absorber 120-1, aliquid pump 120-2, a first heat exchanger 120-3 and a first, or lowtemperature, generator 120-4. The first absorber has an inlet fordelivering the refrigerant vapor, where it is combined with a mixture ofrefrigerant and a first absorbent with a low refrigerant-contentdelivered via line 125, to form a first-absorbent/refrigerant mixturewith a high refrigerant-content. The first absorbent may be or maycontain an ionic compound. The absorption of the refrigerant into theabsorbent also, in general, generates heat (heat of absorption). Coolingwater moves through the tube bundles (not shown) of the absorber toremove this heat of absorption from the system. The highrefrigerant-content mixture collects at the bottom of the firstabsorber, so that the first absorption circuit cycle can begin again.

The high refrigerant-content first-absorbent/refrigerant mixture exitsfrom the first absorber through an outlet line 121 and is sent to theliquid pump, 120-2, which pumps the said mixture to the first heatexchanger 120-3. The first heat exchanger 120-3, which may be a shelland tube type heat exchanger, pre-heats the said mixture before itenters the first (or low temperature) generator 120-4. After exiting theheat exchanger, the said mixture flows into the first generator througha line 122. The first generator is supplied with low-temperature heatfrom any suitable external source. In one embodiment, within thegenerator is a bundle of tubes (not shown) which carry hot water, steam,or combustion gases, which are supplied to the first generator via aline 123. The hot water, steam or combustion gases transfer heat intothe high refrigerant-content first-absorbent/refrigerant mixture. Theheat causes the said mixture to release refrigerant vapor, which exitsfrom the first generator through a line 126, leaving a lowrefrigerant-content mixture behind. The refrigerant is now a higherpressure vapor. In some instances, there is only trace refrigerant leftin the liquid mixture exiting the first generator via line 124. In otherinstances some non-negligible amount of refrigerant remains in thefirst-absorbent/refrigerant mixture exiting the first generator, saidamount ranging from about 1 weight percent to about 80 weight percent.In any case, the amount of refrigerant in the mixture exiting the firstgenerator via line 124 is lower than in the mixture that exited thefirst absorber via line 121. The exact amount of refrigerant remainingin the mixture exiting the first generator will depend on many factorsincluding the solubility of the refrigerant in the first absorbent.

The low refrigerant-content first-absorbent/refrigerant mixture flowsvia line 124 back to the first heat exchanger where it is cooled by thehigh refrigerant-content first-absorbent/refrigerant mixture, which hasbeen pumped out of the first absorber. The low refrigerant-contentfirst-absorbent/refrigerant mixture flows from the first heat exchangerthrough an expansion or pressure reduction device 120-5 to the firstabsorber via a line 125 and collects in the bottom of the first absorberwhere it started the first absorption circuit cycle, and the cycle inthe first absorption circuit repeats.

The second absorption circuit includes a second absorber 130-1, a secondliquid pump 130-2, a second heat exchanger 130-3 and a second, or hightemperature generator 130-4. As noted above, the refrigerant vapor fromthe first absorption circuit exits the first generator and is deliveredto the second absorption circuit via a line 126. The refrigerant vaporis delivered to second absorber 130-1, which includes tube bundles (notshown). A low refrigerant-content mixture of refrigerant and a secondabsorbent is also delivered to the second absorber via line 135. Therefrigerant and the second absorbent collect in the bottom of the secondabsorber. Lithium bromide may be used as the second absorbent in thissystem, it being understood that the present invention is not limited tothe use of lithium bromide as the second absorbent. Again, as in thefirst absorber the refrigerant vapor is absorbed into the lowrefrigerant-content second-absorbent/refrigerant mixture, thus forming ahigh refrigerant-content second-absorbent/refrigerant mixture. Theabsorption of the refrigerant into the absorbent also, in general,generates heat (heat of absorption). Cooling water moves through thetube bundles of the second absorber to remove this heat of absorptionfrom the system.

Second pump 130-2 pumps the high refrigerant-contentsecond-absorbent/refrigerant mixture via a line 131 to the second heatexchanger 130-3, which, like the first heat exchanger, may be a shelland tube type heat exchanger. The second heat exchanger pre-heats thesaid mixture before it enters the second generator 130-4 via a line 132.The second generator is supplied with high-temperature heat from anysuitable external source. In one embodiment, within the second generatoris a bundle of tubes (not shown) which carry combustion gases, steam, orhot water which are supplied to the generator via a line 133. Thecombustion gases, steam or hot water transfer heat into the highrefrigerant-content second-absorbent/refrigerant mixture. The heatcauses the mixture to release refrigerant vapor, which exits from thesecond generator through a heat recovery line 136 a, leaving a lowrefrigerant-content mixture behind in the second generator. Therefrigerant is now a high pressure vapor, which exits the secondgenerator via line 136 a. The heat recovery line extends between thesecond generator and through the first generator, and recovers heat fromthe refrigerant exiting the second generator. In this embodiment, all ofthe high pressure refrigerant vapor is sent back to the first, or lowtemperature generator 120-4, instead of to the condenser. Some of theheat from the high pressure refrigerant vapor is recovered andtransferred to the first generator, instead of being rejected at thecondenser, as in the first embodiment. This results in higher energyefficiency. The heat recovery line continues from the first generator tothe condenser for delivering the refrigerant vapor to the condenser. Thehigh pressure refrigerant vapor is thus sent to the condenser via a line136 b.

The low refrigerant-content second-absorbent/refrigerant mixture flowsvia line 134 back to the second heat exchanger where it is cooled by thehigh refrigerant-content second-absorbent/refrigerant mixture, which hasbeen pumped out of the second absorber to the second heat exchanger. Thelow refrigerant-content second-absorbent/refrigerant mixture flows fromthe second heat exchanger through an expansion or pressure reductiondevice to the second absorber via a line 135 and collects in the bottomof the second absorber, where it started the second absorption circuitcycle, and the second absorption circuit cycle repeats.

The high pressure refrigerant vapor flows to the condenser 110-2 asshown in FIG. 2. In the condenser, cooling water flows through tubes(not shown) in the condenser, and the refrigerant vapor condenses toform refrigerant liquid on the outside of the tubes that collects in atrough (not shown) at the bottom of the condenser. The refrigerantliquid exits from the condenser trough via inlet line 114 to theevaporator through an expansion or pressure reduction device 110-3 thatpartially evaporates the refrigerant liquid. The partially evaporatedrefrigerant liquid contacts the tubes of the evaporator which have wateror some other heat transfer fluid flowing therethrough. The heattransfer fluid is cooled as the liquid portion of the refrigerant isevaporated forming refrigerant vapor. The cooled heat transfer fluid iscirculated back to a body to be cooled, such as a building, thusproviding the cooling effect as desired for instance for airconditioning. The refrigerant vapor migrates to the first absorber fromthe evaporator, and the overall refrigerant cycle repeats.

The use of the configuration in FIG. 2 for heating is also within thescope of the present invention. The only difference in FIG. 2 relativeto FIG. 1 is the line that leads the working fluid vapor exiting thehigh-temperature Generator II (130-4) to the lower temperature GeneratorI (120-4) where the working fluid provides some of its heat to the lowertemperature Generator I (120-4) before it condenses in the condenser(110-2). The heat released upon condensation in the condenser 110-2 isnow used for heating rather than being rejected to the ambient (whichwas the case in the cooling mode of cycle operation). In the heatingmode of cycle operation, an external heat source is used in place of abuilding 110-4 as shown in FIG. 2. Again, in this embodiment, there isno longer exchange of heat between chilled water and a building to becooled, but rather between the water or heat transfer fluid thatsupplies heat to the evaporator and the external heat source. Ingeneral, the option of redistributing heat from the high temperaturegenerator to the low temperature generator in the embodiment of FIG. 2may allow more optimum use of available heat sources in some cases.

In either the embodiment of FIG. 1 or of FIG. 2 where the absorptioncycle is an absorption heating system as discussed above, the use ofabsorbent solutions in the first (low-temperature) absorber that resistcrystallization at low temperatures and, therefore, allow operation ofthe first absorber at temperatures closer to the cold ambienttemperatures during the heating season, could enable dramatically higherenergy efficiencies. Such absorbent solutions that resistcrystallization at low temperatures are disclosed in U.S. ProvisionalPatent Application Ser. Nos. 61/112,415 and 61/112,428 both filed Nov.7, 2008 and 61/165,089, 61/165,093, 61/165,147, 61/165,155, 61/165,161,61/165,160, 61/165,166, and 61/165,173, all of which were filed Mar. 31,2009; each of the foregoing being by this reference incorporated in itsentirety as a part hereof for all purposes. They include compositionscontaining LiBr, water and inorganic salts, wherein the inorganic saltshave been shown to lower the temperature at which LiBr crystallizationproduces system failures. The LiBr crystallization temperaturesuppressants include but are not limited to cesium formate, and otherGroup I metal salts, phosphonic acid salts, and ionic liquids comprisingfluorinated anions, cations or both.

These crystallization resistant compositions were based primarily onusing water as the refrigerant. It should be noted that the phasediagram of the working fluid used in the absorption cycle of thisinvention should allow the coexistence of vapor and liquid phases inequilibrium in the evaporator at temperatures lower than thetemperatures at which heat is extracted from the external sources. Inother words, the triple point temperature of the working fluid should belower than the temperature at which external heat is supplied to theevaporator.

The triple point temperature of water is 0.0098° C. Therefore, whenwater is used as the refrigerant and the absorption cycle is to be usedfor heating when the temperature of ambient air drops below 0.0098° C.,or more practically, below, say, 4° C., the heat supplied to theevaporator must be harvested from sources external to the system otherthan ambient air. External heat sources available at temperatures higherthan the water triple point temperature include, the ground below theearth's surface, natural bodies of water (e.g. water at the bottom of anearby lake or pond), and low temperature process waste heat.

Refrigerant/Absorbent Pairs: Refrigerants:

The present invention provides refrigerant pair compositions for use inan absorption cycle, which can be used for cooling, or for transferringheat from outside to inside, depending on the application. In oneembodiment, water is used as a refrigerant in this invention. In anotherembodiment, the refrigerant may be a hydrofluorocarbon, ahydrochlorofluorocarbon, a chlorofluorocarbon, a fluorocarbon, achlorocarbon, nitrogen (N₂), oxygen (O₂), carbon dioxide (CO₂), ammonia(NH₃), nitrous oxide (N₂O), argon (Ar), hydrogen (H₂), a non-fluorinatedhydrocarbon, or mixtures thereof, meaning mixtures of any of theforegoing refrigerants in this paragraph. The non-fluorinatedhydrocarbons are selected from the group consisting of C₁ to C₇straight-chain, branched or cyclic alkanes and C₁ to C₇ straight-chain,branched or cyclic alkenes, are within the scope of this invention aswell.

Hydrofluorocarbon refrigerants may include compounds having anycombination of hydrogen and fluorine with carbon and include compoundswith at least one carbon-carbon double bond. Examples ofhydrofluorocarbon refrigerants useful for the invention include but arenot limited to difluoromethane (HFC-32), fluoromethane (HFC-41),pentafluoroethane (HFC-125), 1,1,2,2-tetrafluoroethane (HFC-134),1,1,1,2-tetrafluoroethane (HFC-134a), 1,1,1-trifluoroethane (HFC-143a),1,1-difluoroethane (HFC-152a), fluoroethane (HFC-161),1,1,1,3,3-pentafluoropropane (HFC-245fa), 1,1,1,3,3,3-hexafluoropropane(HFC-236fa), 1,1,1,2,3,3-hexafluoropropane (HFC-236ea),1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea),1,1,1,3,3-pentafluorobutane (HFC-365mfc),1,1,1,2,3,4,4,5,5,5-decafluoropentane (HFC-43-10mee),1,1,1,2,2,3,4,5,5,6,6,7,7,7-tetradecafluoroheptane (HFC-63-14mcee),1,2-difluoroethene (HFO-1132), 2,3,3,3-tetrafluoropropene (HFO-1234yf),1,3,3,3-tetrafluoropropene (HFO-1234ze), 1,2,3,3-tetrafluoropropene(HFO-1234ye), 3,3,3-trifluoropropene (HFO-1243zf),1,2,3,3,3-pentafluoropropene (HFO-1225ye), 1,1,1,3,3-pentafluoropropene(HFO-1225zc), 1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336m/z),1,1,1,2,2,5,5,5-octafluoro-2-pentene (HFO-1438mczz),1,1,1,2,2,4,5,5,6,6,7,7,7-tridecafluoro-3-heptene (HFO-162-13mczy) and1,1,1,2,2,3,5,5,6,6,7,7,7-tridecafluoro-3-heptene (HFO-162-13mcyz), andmixtures thereof. In one embodiment of the invention, thehydrofluorocarbon refrigerants are selected from the group consisting ofdifluoromethane (HFC-32), pentafluoroethane (HFC-125),1,1,1,2-tetrafluoroethane (HFC-134a), 1,1,1-trifluoroethane (HFC-143a),1,1-difluoroethane (HFC-152a), 2,3,3,3-tetrafluoropropene (HFO-1234yf),and mixtures thereof.

Additionally, in another embodiment, hydrofluorocarbon refrigerants mayinclude 2-chloro-3,3,3-trifluoropropene (HCFO-1233xf, CF₃CCl═CH₂), cis-or trans-1-chloro-3,3,3-trifluoropropene (HCFO-1233zd, CF₃CH═CHCl),3,4,4,4-tetrafluoro-3-trifluoromethyl-1-butene ((CF₃)₂CFCH═CH₂,HFO-1447fzy), cis- or trans-1,1,1,4,4,5,5,5-octafluoro-2-pentene(CF₃CF₂CH═CHCF₃, HFO-1438m/z), and combinations thereof.

Chlorofluorocarbon refrigerants may include compounds having anycombination of chlorine and fluorine with carbon and include compoundswith carbon-carbon double bonds. Representative chlorofluorocarbonrefrigerants useful for the invention include but are not limited todichlorodifluoromethane (CFC-12), fluorotrichloromethane (CFC-11),1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113),1,2-dichloro-1,1,2,2-tetrafluoroethane (CFC-114) and mixtures thereof.

Hydrochlorofluorocarbon refrigerants may include compounds with anycombination of hydrogen, chlorine and fluorine with carbon and includecompounds with carbon-carbon double bonds. Representativehydrochlorofluorocarbon refrigerants useful for the invention includebut are not limited to chlorodifluoromethane (HCFC-22),2-chloro-3,3,3-trifluoropropene (HCFO-1233xf),1-chloro-3,3,3-trifluoropropene (HCFO-1233zd), and mixtures thereof.

Fluorocarbon refrigerants may include compounds with any combination offluorine and carbon and include compounds with carbon-carbon doublebonds, as well as cyclic compounds. Examples of fluorocarbonrefrigerants useful for the invention include but are not limited toperfluoromethane (FC-14), perfluoroethane (FC-116), perfluoropropane(FC-218, perfluorocyclobutane (FC-C318), octafluoro-2-butene(FO-1318my), and mixtures thereof.

Chlorocarbon refrigerants may include compounds with only chlorine,carbon and optionally hydrogen. Examples of chlorocarbon refrigerantsinclude but are not limited to 1,2-dichloroethylene, methylene chloride,trichloroethylene, perchloroethylene, and mixtures thereof.

Non-fluorinated hydrocarbon refrigerants useful for the invention mayinclude but are not limited to methane, ethane, ethylene, propane,cyclopropane, propylene, n-butane, butane, isobutane, cyclobutane,n-pentane, isopentane, n-hexane, cyclohexane, n-heptane, and mixturesthereof.

In some embodiments, mixtures of the various classes of refrigerants areintended to be included in the scope of the present invention.Additionally, azeotrope and azeotrope-like compositions formed by 2 ormore of the many refrigerants disclosed herein may be particularlyuseful in the present absorption cycle systems.

In another embodiment, the hydrofluorocarbon working fluids may comprisemixtures or blends of hydrofluorocarbons with other compounds such ashydrofluorocarbons, hydrochlorofluorocarbons, hydrocarbons or othercompounds. Such working fluid blends include the following compositions:

HFO-1447fzy with at least one compound selected from the groupconsisting of cis- or trans-HFO-1438m/z, cis- or trans-HFO-1336m/z,HCFO-1233xf, and cis- or trans-HCFO-1233zd;

cis-HFO-1438m/z with at least one compound selected from the groupconsisting of trans-HFO-1438m/z, cis- or trans-HFO-1336m/z, HCFO-1233xf,and cis- or trans-HCFO-1233zd;

trans-HFO-1438m/z with at least one compound selected from the groupconsisting of cis- or trans-HFO-1336m/z, HCFO-1233xf, cis- ortrans-HCFO-1233zd, and isopentane;

cis-HFO-1336m/z with at least one compound selected from the groupconsisting of trans-HFO-1336m/z, HCFO-1233xf, cis- or trans-HCFO-1233zd,isopentane, n-pentane, cyclopentane, methyl formate,1,1-dichloro-2,2,2-trifluoroethane (HCFC-123), andtrans-1,2-dichloroethylene; trans-HFO-1336m/z with at least one compoundselected from the group consisting of HCFO-1233xf, and cis- ortrans-HCFO-1233zd;

HCFO-1233xf with at least one compound selected from the groupconsisting of cis- and trans-HCFO-1233zd.

In another embodiment, working fluids that are mixtures may be azeotropeor azeotrope-like compositions such as the following:

about 51 weight percent to about 70 weight percent cis-HFO-1336m/z andabout 49 weight percent to about 30 weight percent isopentane;

about 62 weight percent to about 78 weight percent cis-HFO-1336m/z andabout 38 weight percent to about 22 weight percent n-pentane;

about 75 weight percent to about 88 weight percent cis-HFO-1336m/z andabout 25 weight percent to about 12 weight percent cyclopentane;

about 25 weight percent to about 35 weight percent cis-HFO-1336m/z andabout 75 weight percent to about 65 weight percent HCFC-123;

about 67 weight percent to about 87 weight percent cis-HFO-1336m/z andabout 33 weight percent to about 13 weight percenttrans-1,2-dichloroethylene; and

about 61 weight percent to about 78 weight percent trans-HFO-1438m/z andabout 39 weight percent to about 22 weight percent isopentane.

In one embodiment, a refrigerant as used herein may also be selectedfrom the group consisting water, and mixtures of water with HFC-32,HFC-125, HFC-134, HFC-134a, HFC-143a, HFC-152a, HFC-161, HCFC-22, FC-14,FC-116, CFC-12, NH₃, CO₂, N₂, O₂, H₂, Ar, methane, ethane, propane,cyclopropane, propylene, butane, butene, and isobutane.

Although certain refrigerants are specified above, the inventiveabsorption cycle of this invention could, in general, be advantageousfor any refrigerant or mixture of refrigerants for which two absorbentsare available such that the first-absorbent/refrigerant mixture ispreferable at low temperatures and the second-absorbent/refrigerantmixture is preferable at high temperatures. Preference for anabsorbent/refrigerant mixture for the low temperature absorption circuitcould be the result of various properties of the absorbent/refrigerantmixture over the preferred operating concentration and temperatureranges for the intended application including reduced crystallizationtemperature, advantageous refrigerant absorption/desorption propertiesat low temperatures, reduced viscosity and enhanced heat and masstransfer in the absorber. Preference for an absorbent/refrigerantmixture for the high temperature absorption circuit could be the resultof various properties of the absorbent/refrigerant mixture over thepreferred operating concentration and temperature ranges for theintended application including higher thermal stability, reducedcorrosivity toward materials of equipment construction, advantageousrefrigerant absorption/desorption properties at high temperatures andenhanced heat and mass transfer properties.

Mixtures of refrigerants are also useful for achieving proper boilingtemperature or pressure appropriate for absorption equipment. Inparticular, mixtures that form azeotropes, azeotrope-like mixtures, orconstant boiling mixtures are sometimes preferred because minimal to nofractionation of the mixture will occur if the refrigerant leaks fromthe absorption cooling system.

Absorbents:

In a preferred embodiment of the absorption cycle of this invention, theabsorbent used is an ionic compound, which can in principle be any ioniccompound that absorbs water. A suitable ionic compound that absorbswater is an ionic compound with which at least to some extent water ismiscible, or in which at least to some extent water is soluble ordispersible so as to form an adequately stable emulsion. The energyefficiency of the absorption cycle will, generally, increase withincreased absorptivity of the ionic compound for water (i.e. water hashigh miscibility therewith or water is soluble therein to a largeextent). One such ionic compound is lithium bromide (LiBr).

Many ionic compounds are formed by reacting a nitrogen-containingheterocyclic ring, preferably a heteroaromatic ring, with an alkylatingagent (for example, an alkyl halide) to form a quaternary ammonium salt,and performing ion exchange or other suitable reactions with variousLewis acids or their conjugate bases to form the ionic compound.Examples of suitable heteroaromatic rings include substituted pyridines,imidazole, substituted imidazole, pyrrole and substituted pyrroles.These rings can be alkylated with virtually any straight, branched orcyclic C₁₋₂₀ alkyl group, but preferably, the alkyl groups are C₁₋₁₆groups. Various triarylphosphines, thioethers and cyclic and non-cyclicquaternary ammonium salts may also been used for this purpose.Counterions that may be used include chloroaluminate, bromoaluminate,gallium chloride, tetrafluoroborate, tetrachloroborate,hexafluorophosphate, nitrate, trifluoromethane sulfonate,methylsulfonate, p-toluenesulfonate, hexafluoroantimonate,hexafluoroarsenate, tetrachloroaluminate, tetrabromoaluminate,perchlorate, hydroxide anion, copper dichloride anion, iron trichlorideanion, zinc trichloride anion, as well as various lanthanum, potassium,lithium, nickel, cobalt, manganese, and other metal-containing anions.

Ionic compounds may also be synthesized by salt metathesis, by anacid-base neutralization reaction or by quaternizing a selectednitrogen-containing compound; or they may be obtained commercially fromseveral companies such as Merck (Darmstadt, Germany) or BASF (MountOlive, N.J.).

Representative examples of ionic compounds useful herein included amongthose that are described in sources such as J. Chem. Tech. Biotechnol.,68:351-356 (1997); Chem. Ind., 68:249-263 (1996); J. Phys. CondensedMatter, 5: (supp 34B): B99-B106 (1993); Chemical and Engineering News,Mar. 30, 1998, 32-37; J. Mater. Chem., 8:2627-2636 (1998); Chem. Rev.,99:2071-2084 (1999); and WO 05/113,702 (and references therein cited).In one embodiment, a library, i.e. a combinatorial library, of ioniccompounds may be prepared, for example, by preparing various alkylderivatives of a quaternary ammonium cation, and varying the associatedanions. The acidity of the ionic compounds can be adjusted by varyingthe molar equivalents and type and combinations of Lewis acids.

Ionic compounds that are suitable for use as absorbents include thosehaving cations selected from the following, and mixtures thereof:

Lithium, Sodium, Potassium, Cesium, and the following Formulae:

wherein R¹, R², R³, R⁴, R⁵, R⁶, R¹² and R¹³ are independently selectedfrom the group consisting of:

-   -   (i) H    -   (ii) halogen    -   (iii) —CH₃, —C₂H₅, or C₃ to C₂₅ straight-chain, branched or        cyclic alkane or alkene, optionally substituted with at least        one member selected from the group consisting of Cl, Br, F, I,        OH, NH₂ and SH;    -   (iv) —CH₃, —C₂H₅, or C₃ to C₂₅ straight-chain, branched or        cyclic alkane or alkene comprising one to three heteroatoms        selected from the group consisting of O, N, Si and S, and        optionally substituted with at least one member selected from        the group consisting of Cl, Br, F, I, OH, NH₂ and SH;    -   (v) C₆ to C₂₀ unsubstituted aryl, or C₃ to C₂₅ unsubstituted        heteroaryl having one to three heteroatoms independently        selected from the group consisting of O, N, Si and S; and    -   (vi) C₆ to C₂₅ substituted aryl, or C₃ to C₂₅ substituted        heteroaryl having one to three heteroatoms independently        selected from the group consisting of O, N, Si and S; and        wherein said substituted aryl or substituted heteroaryl has one        to three substituents independently selected from the group        consisting of:        -   (1) —CH₃, —C₂H₅, or C₃ to C₂₅ straight-chain, branched or            cyclic alkane or alkene, optionally substituted with at            least one member selected from the group consisting of Cl,            Br, F I, OH, NH₂ and SH,        -   (2) OH,        -   (3) NH₂, and        -   (4) SH;            R⁷, R⁸, R⁹, and R¹⁰ are independently selected from the            group consisting of:    -   (i) —CH₃, —C₂H₅, or C₃ to C₂₅ straight-chain, branched or cyclic    -   (ii) alkane or alkene, optionally substituted with at least one    -   (iii) member selected from the group consisting of Cl, Br, F, I,        OH, NH₂ and SH;    -   (iv) —CH₃, —C₂H₅, or C₃ to C₂₅ straight-chain, branched or        cyclic    -   (v) alkane or alkene comprising one to three heteroatoms        selected from the group consisting of O, N, Si and S, and        optionally substituted with at least one member selected from        the group consisting of Cl, Br, F, I, OH, NH₂ and SH;    -   (vi) C₆ to C₂₅ unsubstituted aryl, or C₃ to C₂₅ unsubstituted        heteroaryl having one to three heteroatoms independently        selected from the group consisting of O, N, Si and S; and    -   (vii) C₆ to C₂₅ substituted aryl, or C₃ to C₂₅ substituted        heteroaryl having one to three heteroatoms independently        selected from the group consisting of O, N, Si and S; and        wherein said substituted aryl or substituted heteroaryl has one        to three substituents independently selected from the group        consisting of:        -   (1) —CH₃, —C₂H₅, or C₃ to C₂₅ straight-chain, branched or            cyclic alkane or alkene, optionally substituted with at            least one member selected from the group consisting of Cl,            Br, F, I, OH, NH₂ and SH,        -   (2) OH,        -   (3) NH₂, and        -   (4) SH; and            wherein optionally at least two of R¹, R², R³, R⁴, R⁵, R⁶,            R⁷, R⁸, R⁹, and R¹⁰ can together form a cyclic or bicyclic            alkanyl or alkenyl group.

Ionic compounds suitable for use as absorbents include those havinganions selected from the following, and mixtures thereof: [CH₃CO₂]⁻,[HSO₄]⁻, [CH₃OSO₃]⁻, [C₂H₅OSO₃]⁻, [AlCl₄]⁻, [CO₃]²⁻, [HCO₃]⁻, [HCO₂]⁻,[NO₂]⁻, [NO₃]⁻, [SO₄]²⁻, [PO₃]³⁻, [HPO₃]²⁻, [H₂PO₃]¹⁻, [PO₄]³⁻,[HPO₄]²⁻, [H₂PO₄]⁻, [HSO₃]⁻, [CuCl₂]⁻, Cl⁻, Br, F, SCN⁻; BR¹R²R³R⁴,BOR¹OR²OR³OR⁴, carborates (1-carbadodecaborate(1-)), optionallysubstituted with alkyl or substituted alkyl, carboranes(dicarbadodecaborate(1-)) optionally substituted with alkylamine,substituted alkylamine, alkyl or substituted alkyl, and preferably anyfluorinated anion. Fluorinated anions useful herein include [BF₄]⁻,[PF₆]⁻, [SbF₆]⁻, [CF₃SO₃]⁻, [HCF₂CF₂SO₃]⁻, [CF₃HFCCF₂SO₃]⁻,[HCClFCF₂SO₃]⁻, [(CF₃SO₂)₂N]⁻, [(CF₃CF₂SO₂)₂N]⁻, [(CF₃SO₂)₃C]⁻,[CF₃CO₂]⁻, [CF₃OCFHCF₂SO₃]⁻, [CF₃CF₂OCFHCF₂SO₃]⁻, [CF₃CFHOCF₂CF₂SO₃]⁻,[CF₂HCF₂OCF₂CF₂SO₃]⁻, [CF₂₁CF₂OCF₂CF₂SO₃]⁻, [CF₃CF₂OCF₂CF₂SO₃],[(CF₂HCF₂SO₂)₂N]⁻, [(CF₃CFHCF₂SO₂)₂N]⁻; and F⁻. Other suitable anionsinclude those of the Formula:

wherein R¹¹ is selected from the group consisting of:

-   -   (i) —CH₃, —C₂H₅, or C₃ to C₁₀ straight-chain, branched or cyclic        alkane or alkene, optionally substituted with at least one        member selected from the group consisting of Cl, Br, F, I, OH,        NH₂ and SH;    -   (ii) —CH₃, —C₂H₅, or C₃ to C₁₀ straight-chain, branched or        cyclic alkane or alkene comprising one to three heteroatoms        selected from the group consisting of O, N, Si and S, and        optionally substituted with at least one member selected from        the group consisting of Cl, Br, F, I, OH, NH₂ and SH;    -   (iii) C₆ to C₁₀ unsubstituted aryl, or C₃ to C₁₀ unsubstituted        heteroaryl having one to three heteroatoms independently        selected from the group consisting of O, N, Si and S; and    -   (iv) C₆ to C₁₀ substituted aryl, or C₃ to C₁₀ substituted        heteroaryl having one to three heteroatoms independently        selected from the group consisting of O, N, Si and S; and        wherein said substituted aryl or substituted heteroaryl has one        to three substituents independently selected from the group        consisting of:        -   (1) —CH₃, —C₂H₅, or C₃ to C₁₀ straight-chain, branched or            cyclic alkane or alkene, optionally substituted with at            least one member selected from the group consisting of Cl,            Br, F I, OH, NH₂ and SH,        -   (2) OH,        -   (3) NH₂, and        -   (4) SH.

In another embodiment, ionic compounds suitable for use herein may havea cation selected from the group consisting of pyridinium, pyridazinium,pyrimidinium, pyrazinium, imidazolium, pyrazolium, thiazolium,oxazolium, triazolium, phosphonium, ammonium, benzyltrimethylammonium,cesium, choline, dimethylimidazolium, guanidinium, lithium, phosphoniumcholine (hydroxyethyl trimethylphosphonium), potassium, sodium,tetramethylammonium, tetramethylphosphonium, and anions selected fromthe group consisting of, aminoacetate (glycine), ascorbate, benzoate,catecholate, citrate, dimethylphosphate, formate, fumarate, gallate,glycolate, glyoxylate, iminodiacetate, isobutyrate, kojate(5-hydroxy-2-hydroxymethyl-4-pyrone ion), lactate, levulinate, oxalate,pivalate, propionate, pyruvate, salicylate, succinamate, succinate,tiglate (CH₃CH═C(CH₃)COO⁻);, tetrafluoroborate,tetrafluoroethanesulfonate, and tropolonate(2-hydroxy-2,4,6-cycloheptatrien-1-one ion), [CH₃CO₂]⁻, [HSO₄]⁻,[CH₃OSO₃]⁻, [C₂H₅OSO₃]⁻, [AlCl₄]⁻, [CO₃]²⁻, [HCO₃]⁻, [NO₂]⁻, [NO₃]⁻,[SO₄]²⁻, [PO₄]³⁻, [HPO₄]²⁻, [H₂PO₄]⁻, [HSO₃]⁻, [CuCl₂]⁻, Cl⁻, Br⁻, F⁻,SCN⁻, [BF₄]⁻, [PF₆]⁻, [SbF₆]⁻, [CF₃SO₃]⁻, [HCF₂CF₂SO₃]⁻,[CF₃HFCCF₂SO₃]⁻, [HCClFCF₂SO₃]⁻, [(CF₃SO₂)₂N]⁻, [(CF₃CF₂SO₂)₂N]⁻,[(CF₃SO₂)₃C]⁻, [CF₃CO₂]⁻, [CF₃OCFHCF₂SO₃]⁻, [CF₃CF₂OCFHCF₂SO₃]⁻,[CF₃CFHOCF₂CF₂SO₃]⁻, [CF₂HCF₂OCF₂CF₂SO₃]⁻, [CF₂ICF₂OCF₂CF₂SO₃]⁻,[CF₃CF₂OCF₂CF₂SO₃]⁻, [(CF₂HCF₂SO₂)₂N]⁻, [(CF₃CFHCF₂SO₂)₂N]⁻, F⁻, and anyfluorinated anion. Do we cover the various Gen0.5 crystallizationsuppression additives we filed on over the past several months?

In general, water would be expected to be more miscible with or solublein ionic compounds that are hydrophilic to some extent, and ioniccompounds having cations having at least one alcohol side chain, orthose comprising anions having at least one acetate or sulfate group,would thus be desirable choices for use in various embodiments of thisinvention. Water will also preferably be miscible with or soluble in anionic compound as used herein over the temperature range of theoperation of the absorption system, particularly from that of theevaporator to that of the generator. Evaporator temperatures can be aslow as about 5° C. Single effect generator temperatures can be as highas about 150° C., while double effect generator temperatures can be ashigh as about 200° C. As a consequence, over a temperature range of fromabout 5° C. to about 200° C., a variety of different levels of therelative content of the refrigerant and absorbent in an absorption cycleare suitable, and the concentration of either water or an ionic compoundin a composition formed therefrom may be in the range of from about 1%to about 99% by weight of the combined weight of the ionic compound andwater therein.

In various embodiments of this invention, an ionic compound formed byselecting any of the individual cations described or disclosed herein,and by selecting any of the individual anions described or disclosedherein with which to pair the cation, may be used as an absorbent in anabsorption heating or cooling cycle. Correspondingly, in yet otherembodiments, a subgroup of ionic compounds formed by selecting (i) asubgroup of any size of cations, taken from the total group of cationsdescribed and disclosed herein in all the various different combinationsof the individual members of that total group, and (ii) a subgroup ofany size of anions, taken from the total group of anions described anddisclosed herein in all the various different combinations of theindividual members of that total group, may be used as an absorbent. Informing an ionic compound, or a subgroup of ionic compounds, by makingselections as aforesaid, the ionic compound or subgroup will be used inthe absence of the members of the group of cations and/or anions thatare omitted from the total group thereof to make the selection, and, ifdesirable, the selection may thus be made in terms of the members of thetotal group that are omitted from use rather than the members of thegroup that are included for use.

An absorbent as used in an absorption heating or cooling cycle isdesirably a compound that has high solubility for a refrigerant (e.g.,water) and also a very high boiling point relative to the refrigerant.

Although certain absorbents are described above, in general, any twoabsorbents could be used as the first and second absorbents of thepresent invention, as long as the first absorbent is more advantageousat low temperatures (e.g., more resistant to crystallization, or lessviscous), and the second absorbent is more advantageous at hightemperatures (e.g. thermally stable). Either absorbent could (but doesnot have to) contain or consist essentially of an ionic compound, thatis, it could contain or consist essentially of a non-ionic compound.Suitable non-ionic compound absorbents include, but are not limited toethers, esters, amides and ketones.

Mixtures of ionic compounds may also be used herein as the absorbent,and such mixtures may be desirable, for example, for achieving properabsorption behavior, in particular if water is mixed with othercomponents such as alcohols, esters or ethers which maybe used incombination with absorption equipment.

Additives, such as lubricants, corrosion inhibitors, stabilizers, dyes,crystallization inhibitors (such as cesium formate etc.), and otherappropriate materials may be added to the refrigerant pair compositionsuseful for the invention for a variety of purposes provided they do nothave an undesirable influence on the extent to which water is soluble inan ionic compound absorbent. The refrigerant pair compositions of theinvention may be prepared by any convenient method, including mixing orcombining the desired amounts of each component in an appropriatecontainer using, for example, known types of stirrers having rotatingmixing elements.

Cooling water is used in both the absorbers and condenser in theembodiments as described above. For sake of simplicity, the coolingwater streams through the two absorbers and the condenser are not shown.In one embodiment, the cooling water will flow into the first and thesecond absorbers, where it warms due to the heat of absorption of therefrigerant absorbing into the first or second absorbent. From the firstabsorber, the cooling water will flow to the second absorber. From thesecond absorber, the cooling water will flow to the condenser tubebundle, wherein it will provide the cooling to condense the refrigerantvapor to refrigerant liquid. The cooling water is thus heated furtherand flows out of the condenser via a line, not shown, to a cooling toweror other device intended to release the heat picked up in the system tothe surrounding environment and provide cooled water again to thesystem.

The present invention allows for various configurations and approachesfor removing the heat of refrigerant absorption from the two absorbersand removing the heat of refrigerant condensation (and possibly,sub-cooling) from the condenser, and should not be limited to thoseconfigurations specifically described herein.

The present invention allows for various configurations for optimizingenergy management, in general, thereby increasing cycle energyefficiency, and heat recovery, in particular, from the high-temperature,high-pressure refrigerant before said refrigerant rejects heat at thecondenser, it being understood that various configurations with heatrecovery before the condenser are within the scope of the presentinvention.

The present invention allows for various designs for the variousequipment components required for a specific implementation of anabsorption cycle, especially for the absorbers, generators, heatexchangers, and condensers effecting the required heat and mass transferoperations and should not be limited to those designs specificallydescribed herein.

The hot water, steam, or combustion gases supplied to either the firstor the second generator in order to release refrigerant vapor from thefirst- or the second-absorbent/refrigerant mixture may be supplied byany number of sources, including water heated with waste heat from acombustion engine (combustion gases) and solar heated water, amongothers.

In one embodiment, disclosed herein is a process for producing coolingcomprising forming a first-absorbent/refrigerant mixture at a firstabsorber, heating said first-absorbent/refrigerant mixture to releaserefrigerant vapor, sending the refrigerant vapor to a second absorber,forming a second-absorbent/refrigerant mixture, heating thesecond-absorbent/refrigerant mixture to release refrigerant vapor,condensing said refrigerant vapor to form liquid refrigerant,evaporating said liquid refrigerant at a lower pressure in the vicinityof a heat transfer fluid, transferring said heat transfer fluid to thevicinity of a body to be cooled, and reforming the heated first- andsecond-absorbent/refrigerant mixture. By reforming is meant re-dilutingthe concentrated first- and second-absorbent/refrigerant mixturesthrough the absorption of refrigerant vapor to restore the ability ofthe said mixtures to transfer refrigerant to the first and secondgenerators, respectively.

In another embodiment, in a similar manner to the process describedabove to produce cooling, an absorption cycle may be used to generateheat with for instance an absorption heat pump. In this process the heatof absorption generated by absorbing the refrigerant into the absorbentsin the absorbers and, primarily, the heat of condensation generated bycondensing the refrigerant vapor to refrigerant liquid in the condensercan be transferred to water or some other heat transfer fluid, which isused to heat any space, location, object or body.

In addition, the present invention is not limited to only thoseembodiments shown or described herein. For instance, the extension ofthe present invention to cycles where the refrigerant is transferredsuccessively through three absorption circuits connected in series isalso within the scope of the present invention and could be advantageousfor the optimum utilization of heat sources available at three differenttemperatures.

1. An absorption cycle system, comprising: (a) an evaporator forcirculating a refrigerant therethrough; (b) a first absorption circuitdisposed in fluid communication with the evaporator for mixing therefrigerant from the evaporator with a first absorbent, thereby forminga first absorbent and refrigerant mixture and for circulating the firstabsorbent and refrigerant mixture therethrough; (c) a second absorptioncircuit disposed in fluid communication with the first absorptioncircuit for mixing a portion of the refrigerant from the firstabsorption circuit with a second absorbent, thereby forming a secondabsorbent and refrigerant mixture and for circulating the secondabsorbent and refrigerant mixture therethrough; and (d) a condenserdisposed in fluid communication with the second absorption circuit andwith the evaporator.
 2. The system of claim 1, wherein the firstabsorption circuit comprises: (a) a first absorber disposed in fluidcommunication with the evaporator for absorbing the refrigerant from theevaporator into the first absorbent and refrigerant mixture (b) a firstheat exchanger disposed in fluid communication with the first absorberfor receiving and pre-heating the first absorbent and refrigerantmixture from the first absorber, (c) a first liquid pump for pumping thefirst absorbent and refrigerant mixture from the first absorber to thefirst heat exchanger, and (d) a first generator disposed in fluidcommunication with the first heat exchanger for receiving the pre-heatedmixture from the first heat exchanger and transferring additional heatinto the pre-heated mixture.
 3. The system of claim 2, wherein thesecond absorption circuit comprises: (a) a second absorber disposed influid communication with the first generator for absorbing a portion ofthe refrigerant from the first generator into a second mixturecomprising the refrigerant and a second absorbent in the secondabsorber; (b) a second heat exchanger disposed in fluid communicationwith the second absorber for pre-heating the second absorbent andrefrigerant mixture from the second absorber, (c) a second liquid pumpfor pumping the second absorbent and refrigerant mixture from the secondabsorber to the second heat exchanger, and (d) a second generatordisposed in fluid communication with the second heat exchanger forreceiving the pre-heated mixture from the second heat exchanger andtransferring additional heat into the second mixture.
 4. The absorptioncycle system of claim 1, wherein the first absorbent and the secondabsorbent are each an ionic compound.
 5. The absorption cycle system ofclaim 4, wherein the ionic compound comprises a cation and an anion,wherein the cation is selected from the group consisting of: lithium,sodium, potassium, cesium,

wherein R¹, R², R³, R⁴, R⁵, R⁶, R¹² and R¹³ are independently selectedfrom the group consisting of: (a) H (b) halogen (c) —CH₃, —C₂H₅, or C₃to C₂₅ straight-chain, branched or cyclic alkane or alkene, optionallysubstituted with at least one member selected from the group consistingof Cl, Br, F, I, OH, NH₂ and SH; (d) —CH₃, —C₂H₅, or C₃ to C₂₅straight-chain, branched or cyclic alkane or alkene comprising one tothree heteroatoms selected from the group consisting of O, N, Si and S,and optionally substituted with at least one member selected from thegroup consisting of Cl, Br, F, I, OH, NH₂ and SH; (e) C₆ to C₂₀unsubstituted aryl, or C₃ to C₂₅ unsubstituted heteroaryl having one tothree heteroatoms independently selected from the group consisting of O,N, Si and S; and (f) C₆ to C₂₅ substituted aryl or C₃ to C₂₅ substitutedheteroaryl having one to three heteroatoms independently selected fromthe group consisting of O, N, Si and S; and wherein said substitutedaryl or substituted heteroaryl has one to three substituentsindependently selected from the group consisting of: (1) —CH₃, —C₂H₅, orC₃ to C₂₅ straight-chain, branched or cyclic alkane or alkene,optionally substituted with at least one member selected from the groupconsisting of Cl, Br, F I, OH, NH₂ and SH, (2) OH, (3) NH₂, and (4) SH;R⁷, R⁸, R⁹, and R¹⁰ are independently selected from the group consistingof: (a) —CH₃, —C₂H₅, or C₃ to C₂₅ straight-chain, branched or cyclicalkane or alkene, optionally substituted with at least one memberselected from the group consisting of Cl, Br, F, I, OH, NH₂ and SH; (b)—CH₃, —C₂H₅, or C₃ to C₂₅ straight-chain, branched or cyclic alkane oralkene comprising one to three heteroatoms selected from the groupconsisting of O, N, Si and S, and optionally substituted with at leastone member selected from the group consisting of Cl, Br, F, I, OH, NH₂and SH; (c) C₆ to C₂₅ unsubstituted aryl, or C₃ to C₂₅ unsubstitutedheteroaryl having one to three heteroatoms independently selected fromthe group consisting of O, N, Si and S; and C₆ to C₂₅ substituted aryl,or C₃ to C₂₅ substituted heteroaryl having one to three heteroatomsindependently selected from the group consisting of O, N, Si and S; andwherein said substituted aryl or substituted heteroaryl has one to threesubstituents independently selected from the group consisting of: (1)—CH₃, —C₂H₅, or C₃ to C₂₅ straight-chain, branched or cyclic alkane oralkene, optionally substituted with at least one member selected fromthe group consisting of Cl, Br, F, I, OH, NH₂ and SH, (2) OH, (3) NH₂,and (4) SH; and wherein optionally at least two of R¹, R², R³, R⁴, R⁵,R⁶, R⁷, R⁸, R⁹, and R¹⁰ can together form a cyclic or bicyclic alkanylor alkenyl group; and an anion selected from the group consisting of:[CH₃CO₂]⁻, [HSO₄]⁻, [CH₃₀SO₃]⁻, [C₂H₅OSO₃]⁻, [AlCl₄]⁻, [CO₃]², [HCO₃]⁻,[NO₂]⁻, [NO₃]⁻, [SO₄]²⁻, [PO₃]³⁻, [HPO₃]²⁻, [H₂PO₃]¹⁻, [PO₄]³⁻,[HPO₄]²⁻, [H₂PO₄]⁻, [HSO₃]⁻, [CuCl₂]⁻, Cl⁻, Br⁻, I⁻, SCN⁻; BR¹R²R³R⁴,BOR¹OR²OR³OR⁴, carborates optionally substituted with alkyl orsubstituted alkyl, carboranes optionally substituted with alkylamine,substituted alkylamine, alkyl or substituted alkyl, and a fluorinatedanion.
 6. The absorption cycle system of claim 4, wherein therefrigerant comprises water.
 7. The absorption cycle system of claim 4,wherein the refrigerant is selected from the group consisting ofhydrofluorocarbons, hydrochlorofluorocarbons, chlorofluorocarbons,fluorocarbons, chlorocarbons, nitrogen (N₂), oxygen (O₂), carbon dioxide(CO₂), ammonia (NH₃), nitrous oxide (N₂O), argon (Ar), hydrogen (H₂),non-fluorinated hydrocarbons, and mixtures thereof.
 8. The absorptioncycle system of claim 7, wherein the non-fluorinated hydrocarbon isselected from the group consisting of C₁ to C₇ straight-chain, branchedor cyclic alkanes and C₁ to C₇ straight-chain, branched or cyclicalkenes.
 9. The absorption cycle system of claim 7 wherein therefrigerant comprises at least one refrigerant selected from the groupconsisting of difluoromethane (HFC-32), fluoromethane (HFC-41),pentafluoroethane (HFC-125), 1,1,2,2-tetrafluoroethane (HFC-134),1,1,1,2-tetrafluoroethane (HFC-134a), 1,1,1-trifluoroethane (HFC-143a),1,1-difluoroethane (HFC-152a), fluoroethane (HFC-161),1,1,1,3,3-pentafluoropropane (HFC-245fa), 1,1,1,3,3,3-hexafluoropropane(HFC-236fa), 1,1,1,2,3,3-hexafluoropropane (HFC-236ea),1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea),1,1,1,3,3-pentafluorobutane (HFC-365mfc),1,1,1,2,3,4,4,5,5,5-decafluoropentane (HFC-43-10mee),1,1,1,2,2,3,4,5,5,6,6,7,7,7-tetradecafluoroheptane (HFC-63-14mcee),2,3,3,3-tetrafluoropropene (HFO-1234yf), 1,2-difluoroethene (HFO-1132),1,3,3,3-tetrafluoropropene (HFO-1234ze), 1,2,3,3-tetrafluoropropene(HFO-1234ye), 3,3,3-trifluoropropene (HFO-1243zf),1,2,3,3,3-pentafluoropropene (HFO-1225ye), 1,1,1,3,3-pentafluoropropene(HFO-1225zc), 1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336m/z),1,1,1,2,2,5,5,5-octafluoro-2-pentene (HFO-1438mczz),1,1,1,2,2,4,5,5,6,6,7,7,7-tridecafluoro-3-heptene (HFO-162-13mczy) and1,1,1,2,2,3,5,5,6,6,7,7,7-tridecafluoro-3-heptene (HFO-162-13mcyz),dichlorodifluoromethane (CFC-12), fluorotrichloromethane (CFC-11),1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113),1,2-dichloro-1,1,2,2-tetrafluoroethane (CFC-114), chlorodifluoromethane(HCFC-22), 2-chloro-3,3,3-trifluoropropene (HCFO-1233xf),1-chloro-3,3,3-trifluoropropene (HCFO-1233zd), perfluoromethane (FC-14),perfluoroethane (FC-116), perfluoropropane (FC-218, perfluorocyclobutane(FC-C318), octafluoro-2-butene (FO-1318my), 1,2-dichloroethylene,methylene chloride, trichloroethylene, perchloroethylene, methane,ethane, ethylene, propane, cyclopropane, propylene, n-butane, butane,isobutane, cyclobutane, n-pentane, isopentane, n-hexane, cyclohexane,n-heptane, nitrogen (N₂), oxygen (O₂), carbon dioxide (CO₂), ammonia(NH₃), nitrous oxide (N₂O), argon (Ar), hydrogen (H₂), and mixturesthereof.
 10. The absorption cycle system of claim 2, further including afirst recirculation line between the first generator and the first heatexchanger, and between the first heat exchanger and the first absorber,for recirculating the first absorbent and refrigerant mixture back tothe first absorber.
 11. The absorption cycle system of claim 3, furtherincluding a second recirculation line between the second generator andthe second absorber for recirculating the second absorbent andrefrigerant mixture back to the second absorber.
 12. The absorptioncycle system of claim 3, further including a heat recovery lineextending between the second generator and through the first generatorfor recovering heat from the refrigerant exiting the second generator,said heat recovery line continuing from the first generator to thecondenser, for delivering the refrigerant vapor to the condenser. 13.The system of claim 1, wherein the system is an absorption coolingsystem.
 14. The system of claim 1, wherein the system is a heat pump.